3,4,5-trimethylcatechol diester, and its hydrolysed product, trimethylcatechol, have been advantageously used as antioxidants or additives for resins, higher fatty acids, higher alcohols and oils; and raw materials for a monomer, perfumes and pharmaceuticals.
U.S. Pat. No. 3,624,134 discloses that the reaction of .alpha.-isophorone with an acylating agent, in the presence of an acid catalyst, provides 3,5,6-trimethylcatechol diester at a yield of 20%. However, this process also yields by-products in large amounts, thus providing the object compound in poor yield. Besides, the compound cannot be separated and purified in a simple manner. As to 3,4,5-trimethylcatechol diester, this literature makes no reference.
Japanese Patent Application Laid-open No. 7632/1972 (JP-A-47-7632) teaches a method for producing trimethylhydroquinone diester by reacting 2,6,6-trimethylcyclohexe-2-en-1,4-dione (ketoisophorone, KIP) with an acylating agent in the presence of a protonic acid catalyst or a Lewis acid catalyst. Neither in this literature is disclosed 3,4,5-trimethylcatechol diester.